Los Angeles - Robert Downey Jr is still not sure that he will once again play Tony Stark in 'Iron Man 4' but the actor says he would return to the Marvel franchise if old friend Mel Gibson directs it.

Downey Jr says doing the fourth movie will be a way of repaying the 'Braveheart' star for the things he did to help Downey during the self-destructive chapter in his life years ago, reports suggest.

When asked about his future in the Marvel Cinematic Universe if he ends up hanging up his armor suit, Downey Jr said, "That's all being talked about on a bunch of different levels right now." (PTI)